Researchers at the Massachusetts Institute of Technology (MIT) have developed a new method of using 3D printing to produce a metamaterial that is both strong and remarkably stretchable. The technical basis is a microscopic double structure consisting of a rigid support scaffold and a flexible, coiled network architecture. Both components are made from an acrylic-based polymer and produced in a single printing process using two-photon lithography.
Conventional metamaterials are usually based on rigid lattice structures, which are known for their high rigidity and resistance. However, this stability often comes at the expense of flexibility. The MIT researchers led by Carlos Portela specifically looked for a way out of this conflict of objectives and found inspiration in the structure of hydrogels. These soft, water-containing materials combine stiff and flexible molecular networks, which leads to exceptional mechanical resilience.
“We are opening up this new territory for metamaterials,” says Carlos Portela, the Robert N. Noyce Career Development Associate Professor at MIT. “You could print a double-network metal or ceramic, and you could get a lot of these benefits, in that it would take more energy to break them, and they would be significantly more stretchable.
We realized that the field of metamaterials has not really tried to make an impact in the soft matter realm,” he says. “So far, we’ve all been looking for the stiffest and strongest materials possible.”
The newly developed metamaterial can be stretched to three times its length – a value that exceeds the stretchability of conventional grid metamaterials made from the same base material by a factor of ten. The behavior can be further optimized through the targeted arrangement of “defects”, i.e. microscopic holes: Energy absorption increases, crack propagation is inhibited.
“Think of this woven network as a mess of spaghetti tangled around a lattice. As we break the monolithic lattice network, those broken parts come along for the ride, and now all this spaghetti gets entangled with the lattice pieces,” Portela explains. “That promotes more entanglement between woven fibers, which means you have more friction and more energy dissipation.”
A decisive factor is the interaction between the rigid and flexible structures during stretching. The researchers observe increased mechanical entanglement and energy distribution, which improves structural integrity.
“You might think this makes the material worse,” says study co-author Surjadi. “But we saw once we started adding defects, we doubled the amount of stretch we were able to do, and tripled the amount of energy that we dissipated. That gives us a material that’s both stiff and tough, which is usually a contradiction.”
The research group sees potential applications in tear-resistant textiles, flexible electronic housings or biocompatible scaffolds for tissue regeneration. In the long term, the design could be transferred to ceramic or metallic materials to give them new mechanical properties. The results were published in Nature Materials.
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